1. Field of the Invention
The present invention relates to a means for controlling the infestation of buildings by insect pests, particularly by subterranean insect pests. More particularly, the present invention is a flexible membrane disposed as a liner in an excavation prior to the construction of a building therein, and which includes an array of connected porous tubes for the delivery of insecticide to all parts of the membrane both upon initial installation and subsequently during the useful lifetime thereof.
2. Description of the Prior Art
Insect pest control devices comprising some form of bonded textile fibers coated with an insecticide are known in the art. For example, U.S. Pat. No. 4,103,450 to Whitcomb shows an insecticidal device, which uses a lofty bonded web of textile fibers as a scaffold for insecticidal materials, which may subsequently volatilize therefrom into the ambient air. The device purports to permit control over the location, distribution and dispersal of the volatile insecticide deployed therein, and may be simply discarded when the quantity of the insecticide remaining therein falls below an effective level. The device is said to have a number of advantages, particularly for household applications, because it may be deployed readily in small spaces behind appliances which may attract insects. Because the insects in question may actually crawl through the interstices between the textile fibers in the lofty assembly, thereby coming into prolonged direct physical contact with the insecticide being used, the Whitcomb device is highly efficient in its use of the insecticide.
The emphasis in the Whitcomb patent is on a lofty, resilient, highly porous structure which provides an effective, but temporary, means of controlling domestic insect pests in the interior of a house. However, the solution to problems encountered in exterior, or outdoor, insect control requires a totally different approach. For example, in many parts of the world, termites are endemic, and, as cellulose forms their principal food material, they can cause a great deal of damage to wooden structures. Typically, termite colonies build nests underground in the soil near ground level, in a stump or other source of timber, or in the trunk of a living tree. Colonies may persist for years and may attain populations running into millions of individuals.
Termite attacks originate from the nest. Timber lying on or buried, partially or completely, in the ground may be reached by underground foraging galleries. Attacks may also be carried out well above the ground surface via access passages constructed by the termites from mud or earth on a concrete or brick building foundation.
Both a building and its contents may be provided with significant protection by means of a chemical soil barrier which prevents the attacking termites from reaching wooden structural members. The conventional practice is to treat the soil surrounding a building foundation and footing with any one of a number of well-known chemicals. Chemicals such as aldrin, chlordane, dieldrin and heptachlor may be sprayed on the soil surface by low pressure spray equipment. Alternatively, vertical chemical barriers may be installed by excavating trenches, by treating the exposed trench and by refilling the trench with treated soil, or by rod injection.
In addition to spraying soil with toxic chemicals, other practitioners in the field have proposed insecticidal barriers, including barriers against termites for use around building structures. For example, U.S. Pat. No. 2,899,771 discloses a flexible vapor barrier carrying a layer of water-emulsifiable insecticide. The insecticide in question is carried in a flexible, relatively thin, water-soluble substance, such as "Polyox". U.S. Pat. No. 2,139,225 shows a paper which is coated with arsenate of lead mixed into a paint, whose base is mineral pitch or asphalt. A felt paper in sheet form is impregnated with the mixture by application to one or both surfaces thereof. After the paper has dried, it is packaged and thereafter may be used whenever desired in the same manner as ordinary felt paper, i.e., it can be laid under floors, or placed between foundations and superstructures, or between the walls of buildings and roofs.
An interesting alternative approach to the provision of an effective termite barrier for new construction is described in International Patent Publication No. WO 90/14004. This publication describes a method of preventing termite damage by providing at the building site a flexible, untreated blanket which is used, for example, to line a building excavation, and then is impregnated with a suitable insecticide. The new construction is then built over the impregnated blanket. The fiber assembly is not described in great detail in this publication. In particular, International Patent Publication No. WO 90/14004 teaches nothing about the fiber density of the fiber assembly, or about its void volume.